Best Carbon Monoxide Detectors in 2025: High-Grade CO Protection

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When choosing home detectors and alarms, it's vital to include features that can sense CO (carbon monoxide) levels, since that insidious gas is colorless, odorless and tasteless, and has been responsible for many accidental deaths -- especially in colder seasons when more heating is needed. That's why at CNET, we've tested and reviewed all kinds of detectors that both include and specialize in monitoring CO, and provide timely alerts when the dangerous gas is present.

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Best Carbon Monoxide Detectors in 2025: High-Grade CO Protection
What is the best carbon monoxide detector overall?
Best carbon monoxide detector of 2025
Best overall carbon monoxide detector
Best wired carbon monoxide detector
Best plug-in carbon monoxide detector
Best portable carbon monoxide detector
How we test carbon monoxide detectors
Other carbon monoxide detectors we've tested
Factors to consider when buying a carbon monoxide detector

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What is the best carbon monoxide detector overall?

A First Alert CO detector on a white wall.

Out of all the models we tested, we preferred to combine the well-testing sensors on the First Alert SC5 detector with its smart support for the Google Home app, which adds many phone-based advantages. Plus, it's a battery model, so you can put it nearly anywhere you're worried about CO gas leaks. We also chose options for portable detectors, plug-in models and hardwired versions so you have your pick based on your needs.

Best carbon monoxide detector of 2025

Pros

CO and smoke sensors
First Alert performs well in our tests
Smart features for Google Home
Battery powered for easier placement

Cons

Won't work if codes require a wired sensor
More expense than the average sensor at over $100

First Alert’s detector handles both smoke and CO at the same time, which helps to meet safety codes while giving you the alarms you need. It’s also compatible with the Google Home app thanks to Nest Protect integration. That means it can send phone alarms no matter where you are and give you other important status updates -- an ideal combination of First Alert’s accurate sensors from our testing and Google Home technology.

Even if you don’t want app integration, the detector still offers voice alerts to tell you exactly what it’s sensing. However, note that it is a battery model. On one hand, we like battery options because you can put them right where you’re worried CO leaks may be, even if there are no outlets (like a garage or shed). However, that also means it may not be compliant with all building codes, so you may want to do a little research ahead of time.

Pros

Kidde's sensors test as very reliable
Smart support for Ring and Alexa
Optional professional monitoring service
Voice alerts

Kidde’s smoke/CO detector is similar to First Alert’s option and Kidde alarms also perform very well in our testing, but there are two important differences. First, the smoke alarm is hardwired, not battery-based, so it’s more likely to meeting building code requirements but will need to be installed in the proper location with a bit of wiring work.

Second, this CO detector is also smart, but it’s made to work with Amazon security brand Ring and Alexa. That means you can use the Ring app for smart alerts on your phone or even choose a separate Ring monitoring plan specifically for professional monitoring for your smoke or CO warnings ($5 per month). If you’re more of an Alexa home than a Google Home, this detector may work well for you.

Pros

Simple plug-in model
Smart home support for Google and Alexa
Voice and app alerts
Also measures VOCs

Cons

App setup is a bit complicated for new users
Needs to be in Wi-Fi range

Sometimes what you really want is a smaller CO monitor that you can plug into an outlet and then just leave it alone to do its job, without worrying about replacing batteries or wiring. This Kidde plug-in model is the best we’ve seen, equipped with both voice alarms and app connections with Alexa and Google Home.

Plus, the device extends beyond CO monitoring to track the amount of volatile organic compounds (VOCs) in the air. That makes it very well suited for an outlet near a workbench, crafting table, or home hobby shop. Just note that setup will require juggling a few apps starting with the Kidde app if you want to get all the smart home bells and whistles.

Pros

Portable
Accurate
Sirens at multiple detection levels
Included carry pouch
Runs on AAA batteries

This Klein Tools meter looks professional, but it’s also fit for your home or your pocket, where it can provide accurate CO readings on demand, and sound alarms when CO levels hit both low and high levels. There’s also visual readings and warnings, plus an auto-power off mode to save on battery life.

The meter is small and handy enough to take on trips and camping, or carry in its strap while you’re working on a vehicle or mechanical project. It’s a targeted solution if you’re spending time in areas (especially enclosed areas like tents, cabins, garages, etc.) that could fill with CO gas.

Our test rig for carbon monoxide detectors pumps the hazardous gas directly into an enclosed test chamber.

To put these detectors to the test, we took to the lab and built a test rig designed to measure each unit's response time to varying concentrations of carbon monoxide, specifically at 250 ppm and 400 ppm. Our goal was to determine each detector's respective effectiveness at detecting potentially hazardous levels of carbon monoxide. To declare our winners, we also took into account features that add to the overall user experience, performance and cost-efficiency of each unit.

For the 250 ppm concentration level, we try to simulate a situation where carbon monoxide has begun to build up to hazardous levels. We test twice at this concentration and average the results. At 400 ppm, we replicate a worst-case scenario, a potentially deadly situation, and give the units a pass or fail score. Spoiler alert: They will all save your life, which goes to show how important it is to have carbon monoxide detectors installed on every floor of your home.

This is one of the most dangerous tests we've ever conducted. Carbon monoxide exposure is no joke. It's virtually undetectable and, well, quite deadly. We needed to create a safe way of testing carbon monoxide detectors without risking the health and safety of our laboratory staff. So I made use of my rudimentary carpentry skills and built a carbon monoxide detector test station. Its components are:

Carbon monoxide detector chamber: Made using wood, plexiglass, silicon, tape and a bunch of finish nails.

Carbon monoxide tank with gas flow regulator: Cylinder tank containing carbon monoxide at 2,500 ppm and balance air.

Testo 300 with carbon monoxide Ambient sensor: Our control device for this experiment.

Two portable carbon monoxide gas alarms.

The inside of our carbon monoxide detector test rig.

The chamber houses two carbon monoxide detectors, a) the CO Ambient sensor portion of our control device, the Testo 300, which is a combustion analyzer used by heating engineers who carry out installation and routine maintenance of industrial and residential heating systems, and b) the unit under test, or UUT, which takes the place of each carbon monoxide detector we tested for you. The chamber is sealed with foam but not air-tight, because we're not particularly interested in making a carbon monoxide bomb.

A closer look at the gas regulator on the tank of carbon monoxide used in our carbon monoxide detector tests.

We installed a gas flow regulator on our tank to avoid pressure spikes, followed by a gas line to feed our gas mixture into the chamber. Two additional portable carbon monoxide detectors are used. One near the valve, to ensure there are no leaks and another that must be worn by the person experimenting to make sure there is no carbon monoxide buildup in the test station area. On top of all that, our respirator suits and amply ventilated location ensure that we get a constant stream of fresh air at all times. This might all sound excessive, but it's always good laboratory practice to put safety first, especially when you're dealing with such a stealthy and prolific killer.

We start by feeding our gas mixture to the chamber and closely monitoring the carbon monoxide concentration on the Testo. Once the concentration inside our chamber reaches at least 250 ppm or 400 ppm, we stop feeding the gas and start a timer. We want to assess how long the carbon monoxide detectors take to react to those conditions. As you may understand, we wanted to limit our exposure while making sure our results were repeatable.

Our results are summarized in the interactive graph below:

Nest Protect smoke and carbon monoxide alarm (out of stock): A very compelling option for those who don't mind spending a little more in exchange for a range of smart features including location-specific voice alarm, color-coded emergency notifications and smartphone app control for silencing and routine testing. It underperformed its competition in our quickness of response test, with a bottom-three result in the 250 ppm run and last place in the 400 ppm run. Fortunately, it did a better job at quick smoke detection and fire hazards during our most recent round of smoke detector tests.

Kidde KN-COPP-B-LPM battery-operated carbon monoxide alarm: Battery-powered (meaning monitoring won't stop in a power outage), digital display, test/reset and peak carbon monoxide buttons, visual cues for alarm and operational status. Great unit if you want an affordable device that is capable of monitoring real-time carbon monoxide levels as well as battery life. Not the fastest at detecting carbon monoxide (it ranked fourth). Carbon monoxide readouts on its screen are the least accurate of the bunch, at 15% error, which is by no means the end of the world.

X-Sense combination smoke and carbon monoxide alarm (out of stock): This combo unit comes equipped with a 10-year sealed lithium battery and a digital display that shows real-time carbon monoxide concentration, battery level and working status. Second-to-last place in our quickness of response test, detecting carbon monoxide at 250 ppm after 20 minutes. The carbon monoxide concentration monitor is accurate, with less than 5% error. Its LCD is smaller than those of other products in this category, which makes it a little hard to interpret the readouts if you're not close to the device.

Kidde Plug-in KN-COB-DP2 carbon monoxide alarm: A plug-in unit, backed up by two AA batteries. Features a single LED indicator and a test/reset button. Very specific brand and model requirements for battery replacements. The unit does not come with a cord extension so its installation placement is limited to an electrical outlet. Last place in our quickness of response test.

Ensure it has the right sensors

A carbon monoxide detector sits on a wood table

Carbon monoxide detectors work differently than smoke detectors and should have different sensors. Getting the properly equipped carbon monoxide detector is vital for monitoring levels in your home to prevent any kind of potential poisoning. Ideally, you want a detector with an electrochemical sensor as this type tends to handle changes in temperature and humidity variations best. It also does a good job at not reacting to typical household chemicals and odors that could improperly trigger an alarm.

Replacement timing

Many carbon monoxide detectors have a sealed battery and can last years before needing to be replaced. While this is great as a set it and forget it type of situation, it can also lead to forgetting to ensure it is working. When shopping for a CO detector, make sure the options you are considering provide some kind of alert when it is time to replace the device.

Power supply

As I mentioned in the previous section, many carbon monoxide detectors are battery powered, which can be good as you won't have to rely on placing it near an outlet or dealing with electrical wiring. A battery-operated unit also means that should your home lose power, your CO detector will still be working. However, a hardwired detector has the benefit of never worrying if the battery has died and can sometimes offer more features because power supply isn't a major concern. Importantly, states may have laws requiring wired monoxide detectors with backup batteries in certain locations (just as they do for smoke alarms.)

Apple compatibility

Today’s CO detectors can be plenty smart -- if you want them to be.

The latest monoxide detectors can come with connections to apps and voice assistants. That can help you get warnings more easily, even if you aren’t at home, and even connect you with emergency services. That’s why our top picks on this list include connections with platforms like Google Home (and Gemini for Home), Ring and Alexa. However, if those smart features are too intrusive for you, you can choose not use them or pick a model without them.

What's the latest in the carbon monoxide detector industry?

An unpackaged Kidde smoke detector on a marble counter.

Carbon monoxide improvements are focused on integrations with home apps, including Google Home, Ring and Alexa. That gives them capabilities they’ve never had before, notably ways to send alerts to your phone and give you low battery updates instead of just chirping at random. It also allows certain detectors to connect directly to independent monitoring programs if you want to pay for professional monitoring.

Carbon monoxide detectors work by using sensors to detect the presence of carbon monoxide in the air. When carbon monoxide levels reach a certain threshold, the detector sounds an alarm to alert occupants of the building. There are different types of detectors available, but most use electrochemical sensors, metal oxide semiconductors or biomimetic sensors to detect carbon monoxide.

Carbon monoxide detectors should be placed on every level of the home and in every sleeping area. They should also be placed near sources of potential carbon monoxide, such as furnaces, water heaters, fireplaces and attached garages. Follow the manufacturer's instructions for the specific placement of your detector.

Carbon monoxide detectors should be replaced every five to seven years, depending on the manufacturer's recommendations. Regular testing and maintenance are also important to ensure that the detector is functioning properly and providing adequate protection.

Never ignore carbon monoxide alarms. If your carbon monoxide detectors go off, evacuate the building immediately and seek fresh air. Call the fire department or emergency services from a safe location, and do not re-enter the building until it has been checked and declared safe.

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